1. Field of the Invention
The invention relates to control valve devices in general, and more particularly to a control valve device which controls fluid communication in fluid passages by a piezo-electric element which replaces a conventional electromagnetic mechanism. For example, this invention relates to control valve devices which are applied to change over use etc. of an air pressure device of an automobile.
2. Discussion of the Background
In a typical instance of a conventional control valve device of this type which is broadly utilized for the automobiles etc., there is a control valve device shown in FIG. 2.
As this control valve device, an electromagnetic valve having two change over position has been used. In this control valve device, a solenoid coil 1 is provided around an iron core 2 fixed to a body 9, and a plunger 3 is movably provided near the front end of the iron core 2 through a compression spring 7. In the center of the opposite end surface of the plunger 3 relative to the iron core 2, a seal surface 4 is formed by an element made of rubber etc. One input port 5a provided to the body 9 is normally blocked by the seal surface 4. The iron core 2 is provided with an axial bore which constitutes an other input port 5b.
The other hand, the body 9 is provided with an output port 6 in its part which communicates with a chamber receiving the plunger 3.
In the control valve device having the above construction, when the solenoid coil 1 is not electrically charged, the iron core 2 is not excited. As a result, the plunger 3 is pushed toward the left in FIG. 2 by the force of the spring 7 and blocks the one input port 5a by its seal surface 4. In this case, the other input port 5b communicates with the outlet port 6 through the gaps between the plunger 3 and the iron core 2, and between the body 9 and the plunger 3.
Next, when the electric current is applied to the solenoid coil 1, the iron core 2 is excited and pulls the plunger 3 by magnetic flux generated around the solenoid coil 1 through the body, a yoke 8, the plunger 3 and the iron core 2. Therefore, the seal surface 4 is separated from the one input port 5a so that the one input port 5a and the output port 6 communicate with each other.
In this kind of electromagnetic valve, as mentioned above, the change over operation of the valve member is performed by the initiation and termination of the application of electrical current to the solenoid coil 1. Therefore, the communication between two of the three ports is selectably changed over. So far as the control device is constituted as an electromagnetic valve, however, it is impossible to avoid the following disadvantages.
Namely, in the electromagnetic valve, the solenoid coil 1 consists of a winding, the iron core 2, the plunger 3 comprising a movable iron core and the yoke 8, all of which are indispensable elements of a magnetic circuit. As a result, the number of parts of the control valve device increases and the weight of the control valve device cannot but increase too.
Furthermore, when it is necessary that the plunger 3 is pulled to open the port 5a, it is necessary that the solenoid coil 1 is electrically excited as long as the plunger 3 is to be pulled. Therefore, the consumption of electric power in the control valve device increases.
Furthermore, in this electromagnetic valve, when it is installed in a pipe, it is not able to directly connect with the pipe since its weight is large. Therefore it is not only necessary to securely fix the control valve device to a fixed member such as a bracket but also considerable space for installation is required and the installation environment is bad.